1. Field of the Invention
Embodiments of the present invention relate to a switch apparatus, and more particularly to a switch apparatus in which a plurality of pairs of contacts are closed or opened individually from one another or in a predetermined relation with one another.
2. Description of Related Art
There are a variety of switch apparatuses for electronic equipments. A type of switch apparatus for an electronic equipment has a plurality of switches disposed adjacent to one another. For example, a set of two keys, namely, up and down keys may be used to input numerical values. In general, the two up and down keys are closely located from each other for practical reasons. Since a set of up and down keys is relatively compact for imputing numerical values, as compared with, for example, a ten-key, the set of up and down keys is used for relatively small sized equipment. However, there is a limitation as to how closely the two keys can be located when the equipment is substantially small, such as a wrist watch, in spite of the fact that there are great demands to more closely locate the two keys to one another.
Also, in the field of electronic musical instruments, a multiple-make (for example, two-make) touch response switch has been used for many years. The multiple-make touch response switch has a plurality of fixed contacts and associated movable contacts. By depressing the switch, the plurality of fixed contacts are successively closed by the movable contacts with a time difference that varies depending on the speed of switch depression. For example, a two-make switch has two fixed contacts and two movable contacts. When the switch is depressed, the two fixed contacts are successively closed by the associated movable contacts with a time difference that varies depending on the speed of switch depression.
In such multiple-make switches, the contacts (including both fixed contacts and movable contacts) are located closely to one another. However, any one of the movable contacts should not affect the other movable contacts to achieve a normal switch function of the switch as a whole, even if the switch device is of relatively rough manufacture.
From a functional view point, the structure of the above mentioned two-key switch device allows a pair of switches to turn on and off independently at different specified timings. On the other hand, the structure of the multiple-make switch allows the contacts to turn on and off in a specified relation (a first switch makes contact, and then a second switch makes contact) in association with the switch depression.
In both cases, regardless of the presence or the absense of such a relationship, the requirements are to improve the technology to allow further miniaturization of a switch device that is functional even if the switch is of relatively rough manufacture.
A multiple-make touch response switch, for example, a two-make touch response switch, has a fixed contact and a corresponding movable contact associated with the fixed contact. The fixed contact includes a fixed contact pattern formed on a printed substrate and the movable contact is disposed above and opposing the fixed contact. The movable contact is brought into contact with the fixed contact to perform a switching operation.
FIG. 11 shows part of a prior art two-make switch. FIG. 11 (A) shows a pattern of a fixed contact 46 fromed on a printed substrate 41. FIG. 11 (B) shows a movable contact that is into contact with the fixed contact 46. The fixed contact 46 has two pairs of fixed contact patterns, namely an internal pair of internal patterns 21 and 23, and an external pair of external patterns 22 and 24. Each of the patterns is separated by a specified distance from one another and has a relatively complicated shape as shown in FIG. 11. The patterns 21, 22, 23 and 24 have contact terminals T1, T2, T3 and T4, respectively, formed at their respective terminal ends that connect to an external wiring pattern 30 that is provided external to the switch.
On the other hand, a first movable contact 25 and second movable contacts 26a and 26b are formed above and opposing the fixed contact 46. The first movable contact 25 is provided at a location where the first movable contact 25 comes in contact with end sections of the internal pair to conductively connect the internal patterns 21 and 23. Each of the second movable contacts 26a and 26b is made in the form of an arc, and provided at a location where the movable contacts 26a and 26b connect the external patterns 22 and 24, but do not come in contact with the internal patterns 21 and 23.
The two-make switch of this type is mounted, for example, on each key of an electronic keyboard apparatus to generate a key-on signal or a key depression speed signal in association with the key depression operation.
FIG. 12 shows a circuit diagram of a conventional two-make switch of the type described above. A contact section (the two-make switch) 27 is formed from the fixed contact and the movable contact described above. The contact section 27 includes the four contact terminals T1, T2, T3 and T4. The four contact terminals are connected through, for example, diodes, to four wiring patterns 30 that are formed on a printed substrate external to the switch. Each of the wiring patterns 30 is connected to a CPU (not shown) that is used for generating electronic sound and controlling the timbre, the loudness and other parameters of the musical sound in response to the key depression operation.
FIG. 13 shows two types of two-make switches in cross-section. FIG. 13 (A) shows a two-make switch in which the first movable contact 25 makes first contact with the fixed contact. FIG. 13 (B) shows another two-make switch in which the second contact 26a and 26b make first contact with the fixed contact. The movable contact of the two-make switch 27 is made of an elastic material, such as rubber, a polymeric material, and the like. The movable contact has a depression section 29 formed at its top, a dome-shaped or a cup-shaped elastic deformation section 40, and an edge section 31 along its lower periphery. At the central area within the elastic deformation section 40, there is provided the first movable contact 25 in the form of a circle that is made of a conductive material, and the second movable contacts 26a and 26b in the form of an arc about the first movable contact 25. An elastic protrusion 32 is formed at the lower surface of the edge section 13. The elastic protrusion 32 is pushed through an aperture 33 formed in the printed substrate 41 to fix the switch 27 to the printed substrate 41.
In the switch structure shown in FIG. 13 (A), when the depression section 29 is pressed down, the elastic deformation section 40 deforms itself. As a result, the first movable contact 25 at the center comes in contact with the internal patterns 21 and 23 (see FIG. 11) of the fixed contact formed on the printed substrate 41, and the internal patterns 21 and 23 are conductively connected to each other. By further pressing down the depression section 29, the arc-shaped second movable contacts 26a and 26b come in contact with the external patterns 22 and 24 (see FIG. 11). As a result, the external patterns 22 and 24 are conductively connected to each other. As a consequence, the switch makes contact in two different stages at different timings. In contrast, in accordance with the switch structure shown in FIG. 13 (B), the external second movable contacts 26a and 26b first come in contact with the associated external fixed contacts, and then the first movable contact 25 at the center comes in contact with the associated fixed contacts.
A structure of a typical conventional electronic keyboard apparatus is described in Japanese laid-open patent application HEI 6-176663. The electronic keyboard apparatus shown in this reference has a switch device that is formed from a pair of a movable contacts and a fixed contact for each key. A switch apparatus that is mounted in an electronic keyboard apparatus typically has a structure shown in FIG. 14 or FIG. 15.
As shown in FIG. 14, a two-make switch 50 has a first movable contact 51 and a second movable contact 52, and is mounted on a printed substrate 53. A first fixed contact 54 and a second fixed contact 55 in a comb-teeth pattern are formed on the printed substrate 53 as shown in FIG. 14. The fixed contact 54 is formed from a pair of oppositely engaging comb-teeth patterns 54a and 54b, and the fixed contact 55 is formed from a pair of oppositely engaging comb-teeth patterns 55a and 55b. Each of the comb-teeth shaped fixed contacts 54 and 55 is disposed with ends of the comb patterns being opposed each other. The first and second fixed contacts 54 and 55 are disposed adjacent to each other in a direction in which the comb teeth are arranged. The first and second movable contacts 51 and 52 come in contact with the first and the second fixed contacts 54 and 55, respectively, with a time difference, in a similar manner as the switch structure shown above in FIGS. 11 through 13
In the prior art example shown in FIG. 15, a first fixed contact 54 has a pair of oppositely engaging comb-teeth patterns 54a and 54b, and a second fixed contact 55 has a pair of oppositely engaging comb-teeth patterns 55a and 55b, in a similar manner as the above example shown in FIG. 14. In this example, the fixed contacts 54 and 55 are disposed adjacent and in parallel with each other on a printed substrate in the direction in which the comb teeth are arranged. By this particular structure, the first and second movable contacts 51 and 52 come in contact with the first and the second fixed contacts 54 and 55, respectively, with a time difference, in a similar manner as the above described prior art example.
Switches that successively make contact with a time difference include, for example, a touch response switch that detects key touches in an electronic musical instrument. A typical touch response switch includes a two-make switch. The touch response switch detects the movement of a depressed key based on a time difference between two contacts provided by the two-make switch, computes the key depression speed or the key depression force based on the key depression acceleration, and controls various musical sounds based on these parameters.
On the other hand, a switch apparatus having a plurality of pairs of contacts may be used in a manner other than as a touch response switch in which plural contacts are successively made with a time difference as described above. For example, each of the pairs is provided with two movable contacts having the same height so that the two movable contacts simultaneously come in contact with the associated fixed contact so that each pair functions as an independent switch.
However, in the conventional two-make switches shown in FIGS. 11 through 13, the fixed contact patterns 21, 22, 23 and 24 have the four independent contact terminals T1, T2, T3 and T4. As a result, the manufacture is complicated because the patterns are complicated and thus a fine patterning with a high printing resolution is required. In addition, there are manufacturing limitations in narrowing a separation between adjacent patterns. As a result, a small switch apparatus cannot be manufactured.
Furthermore, a conventional two-make switch may be provided at each key of an electronic keyboard instrument in a manner such that the switch is operated by the key depression operation of each key. Generally, keys of a keyboard instrument are disposed in a manner that each key rotates about one of its ends which acts as a fulcrum, and the switch is disposed in a manner such that the key pushes down the switch by a central area of a lower side of the key as the key is rotated about its fulcrum. As a result, the key does not provide a depression force in a linear, vertical direction with respect to the switch and thus pushes the switch in the course of its rotational movement. As a consequence, the movable contact comes in contact with the fixed contact as the switch is bent and re-bent. Therefore the movement of the movable contact is not stable. As a result, there are occasions in which the first movable contact, that has been in contact with the fixed contact, may separate from the fixed contact when the second movable contact comes in contact with the associated fixed contact pattern, which causes the switch to chatter. As a consequence, where the switch is used as a key touch response detector, sounds are not correctly controlled because correct information of a contact time difference between the two movable contacts is not provided by the switch.
Even if the keyboard structure is modified in a manner that the keys move in the vertical direction, the problem of the switch chattering is not solved. When a key is struck with a strong force, the first movable contact may generate vibrations due to its mass, which may separate the first movable contact from the fixed contact when the second movable contact makes contact with the associated fixed contact.
The above described problems of the prior art technology may occur in the switch structures shown in FIG. 14 and FIG. 15. It is noted that the structures of the prior art switches shown in FIGS. 14 and 15 are exaggerated. More particularly, the contacts 54 and 55 are spaced a greater distance from each other than they are shown in FIGS. 14 and 15. In the prior art structure, the comb-shaped fixed contacts 54 and 55 are disposed as closely as possible from each other to miniaturize the switch. However, for the switch to properly function, the movable contacts are to be positioned with respect to the associated fixed contacts within allowable ranges of S1 and S2 shown in FIG. 14 and FIG. 15 so that each of the movable contacts (for example, the movable contact 52) does not contact a fixed contact (the fixed contact 54) next to the respective associated fixed contact (the fixed contact 55). The allowable ranges are determined by a pitch width between adjacent patterns that is in return determined by the precision of the printing technology for printing the comb teeth patterns. If the patterns are brought closer to each other beyond the allowable range, short circuits occur, and thus the switching function is ruined.
On the other hand, with respect to the movable contacts, the protrusions (the reference numeral 32 in FIG. 13) are formed at a predetermined pitch on the under side of the base section (the end section 31 in FIG. 13) along the key arrangement direction. The protrusions are pushed through the apertures (the reference numeral 33 in FIG. 13) formed in the printed substrate to fix the movable contact to the printed substrate. In this case, there are occasions in which the movable contact is slightly shifted with respect to the fixed contact due to errors in the position and the size of the apertures. It is noted that the allowable ranges S1 and S2 at the fixed contacts 54 and 55 are also determined by the errors described above. As a result, the allowable ranges become much narrower.
The problems described above are associated not only with the use of a touch response switch that detects the key depression force or speed in a keyboard apparatus, but are also associated with switches in general that are formed from a fixed contact pattern and a movable contact pattern. More particularly, the problems are associated with two-make switches and multiple-make switches. Particularly, in switch apparatuses having a plurality of pairs of fixed contacts and opposing movable contacts in which each of the plurality of pairs independently function as a switch, the switches cannot be made smaller and the switches tend to chatter.